System and method for localizing medical instruments during cardiovascular medical procedures

ABSTRACT

A system and method for localizing medical instruments during cardiovascular medical procedures is described. One embodiment comprises an electromagnetic field generator; an antenna reference instrument adapted to be introduced into the heart of a subject and including at least one electromagnetic sensor and at least one electrode; at least one roving instrument adapted to be introduced into the thorax cavity of the subject and including at least one electrode; and a control unit configured to determine position coordinates of the antenna reference instrument based on an electromagnetic signal from the electromagnetic field generator sensed by the electromagnetic sensor, measure an electrical-potential difference between the electrode of the antenna reference instrument and the electrode of the roving instrument, and calibrate the measured electrical-potential difference using the determined position coordinates of the antenna reference instrument to determine position coordinates of the roving instrument.

PRIORITY

This application claims priority, under 35 U.S.C. §119(e), to commonlyowned and assigned U.S. Provisional Patent Application No. 61/622,220,entitled “Integrated Multi-Localizer Cardiovascular Navigation Systemand Associated Method,” which is incorporated herein by reference in itsentirety and for all purposes.

FIELD OF THE INVENTION

The present invention relates generally to systems and methods that aidphysicians in performing surgical procedures on patients. Morespecifically, the invention relates to systems and methods forlocalizing medical instruments within a subject during cardiovascularmedical procedures.

BACKGROUND OF THE INVENTION

Medical procedures to treat cardiovascular diseases are becoming lessinvasive in nature, such that a physician can insert a small medicaldevice into a subject through a small incision and navigate the devicethrough vasculature to the heart and the specific treatment site. Oneresult is that the physician requires specialized tools to see where thedevice is travelling as well as the destination treatment location.Stereotactic navigation is the field of taking pre-acquired images ofthe anatomy of interest and using localization systems to track medicalinstruments with respect to the pre-acquired imaging. Stereotacticnavigation requires position sensing capabilities to be able to locateand track the medical instruments within the human body and display theposition with respect to other medical imagery like x-ray, CT, MRI,ultrasound, and electrocardiogram maps.

Current position sensing systems suffer from several issues. Positionsensing systems need to provide flexibility to localize many differentinstruments based on physician preference, and accuracy in inhomogeneoustissues such as bone, air, blood, muscle, and fat, as those tissuecharacteristics change with breathing and heart beat. The balance ofaccuracy and flexibility is very difficult to achieve. Electromagneticposition sensing systems are often accurate systems because they do notdepend on the tissue characteristics of the living body. However,electromagnetic systems are very proprietary in nature and requireproprietary electromagnetic sensors embedded in every instrument usedduring the procedure that the physician needs to localize.Electrical-potential position sensing systems are typically veryflexible in their ability to track different instruments in an openarchitecture manner using standard electrodes integrated into manymedical instruments. However, the accuracy of electrical-potentialsystems is poor because they are susceptible to the varying tissueimpedance changes due to breathing and heartbeat.

Attempts to combine the accuracy of electromagnetic localization andflexibility of electrical-potential localization have so far failed toprovide a system that overcomes the issues of the separate systems.Current hybrid position sensing systems aim to calibrate a volumelocalized by electrical-potential localization to a volume localized byelectromagnetic localization with a single instrument with respect tobody surface electrodes and use that calibration to track otherinstruments in a common calibrated volume. However, any calibration ofelectromagnetic localization field to electrical-potential localizationfield calculated by the single instrument is valid only at a particularpoint in time correlated with a particular point in a breathing cycleand heart beat cycle or is an average over time that is not particularlyaccurate at any given single point in time. The result is a gatedposition sensing system that is only accurate periodically.

Thus, a need exists for improved systems and methods of localizingmedical instruments within a subject during minimally invasivecardiovascular medical procedures.

SUMMARY OF THE INVENTION

Illustrative embodiments of the present invention that are shown in thedrawings are summarized below. These and other embodiments are morefully described in the Detailed Description section. It is to beunderstood, however, that there is no intention to limit the inventionto the forms described in this Summary of the Invention or in theDetailed Description. One skilled in the art can recognize that thereare numerous modifications, equivalents, and alternative constructionsthat fall within the spirit and scope of the invention as expressed inthe claims.

In one illustrative embodiment, a position sensing system comprises anelectromagnetic field generator; an antenna reference instrument adaptedto be introduced into the heart of a subject, the antenna referenceinstrument including at least one electromagnetic sensor and at leastone electrode; at least one roving instrument adapted to be introducedinto the thorax cavity of the subject, the at least one rovinginstrument including at least one electrode; and a control unitconfigured to determine position coordinates of the antenna referenceinstrument based on an electromagnetic signal from the electromagneticfield generator sensed by the at least one electromagnetic sensor;measure an electrical-potential difference between the at least oneelectrode of the antenna reference instrument and the at least oneelectrode of the at least one roving instrument; and calibrate themeasured electrical-potential difference using the determined positioncoordinates of the antenna reference instrument to determine positioncoordinates of the at least one roving instrument.

Another illustrative embodiment is a method for sensing the position ofa medical instrument, comprising applying an electromagnetic field tothe thorax area of a subject; inserting an antenna reference instrumentinto the heart of the subject, wherein the antenna reference instrumentincludes at least one electromagnetic sensor and at least one electrode;inserting at least one roving instrument into the thorax cavity of thesubject, wherein the at least one roving instrument includes at leastone electrode; determining position coordinates of the antenna referenceinstrument based on sensing the electromagnetic field using the at leastone electromagnetic sensor; measuring an electrical-potential differencebetween the at least one electrode of the antenna reference instrumentand the at least one electrode of the at least one roving instrument;and calibrating the measured electrical-potential difference using thedetermined position coordinates of the antenna reference instrument todetermine position coordinates of the at least one roving instrument.

These and other embodiments are described in further detail herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an antenna reference instrument, according to anillustrative embodiment of the invention.

FIG. 2 illustrates a position sensing system, according to anillustrative embodiment of the invention.

FIG. 3 is a functional block diagram of a control unit for use in aposition sensing system, according to an illustrative embodiment of theinvention.

FIG. 4a illustrates a display for tracking instruments relative to asubject's heart, according to an illustrative embodiment of theinvention.

FIG. 4b illustrates a display for tracking instruments relative to asubject's heart, according to another illustrative embodiment of theinvention.

FIG. 5 is a flowchart of a method for determining the position of aroving instrument, according to an illustrative embodiment of theinvention.

FIG. 6 is a flowchart of a method for determining the position of aroving instrument, according to another illustrative embodiment of theinvention.

FIG. 7 is a flowchart of a method for displaying the position of aroving instrument, according to yet another illustrative embodiment ofthe invention.

FIG. 8 is a flowchart of a method for determining the position of aroving instrument, according to yet another illustrative embodiment ofthe invention.

DETAILED DESCRIPTION OF THE INVENTION

In various illustrative embodiments of the invention, a position sensingsystem used to navigate medical instruments through a patient'scardiovascular system during a cardiovascular procedure includes anantenna reference instrument that can be inserted into the heart of thepatient and localized by at least two different systems. The antennareference instrument can be inserted into a stable location in the heartby the physician and remain there for the duration of the procedure,providing a stable reference point. This reference point ensures thatthe images that the physician is viewing during the procedure areaccurate. The antenna reference instrument can be localized by anelectromagnetic system through its electromagnetic sensor and by anelectrical-potential system through its electrodes. The absolutelocation of the antenna reference instrument is determined by a controlunit using an electromagnetic field sensor that is embedded into theantenna reference instrument and the supporting electromagnetic fieldlocalization system. The absolute location of the antenna referenceinstrument is accurate because the electromagnetic system is notdependent on tissue characteristics, the patient's breathing, or thepatient's heart beating. Additionally, roving instruments that are usedto diagnose diseases and deliver treatments are included. Each rovinginstrument includes electrodes for localization by theelectrical-potential system. Current typical instruments used todiagnose and treat cardiovascular diseases already include electrodes,which makes this a very open-architecture system as it can be used withwidely available instruments that are already on the market. The controlunit can determine the location of any one of the roving instruments bymeasuring the electrical-potential difference between the electrodes onthe antenna reference instrument and the electrodes on the rovinginstrument in question. Because the antenna reference instrumentlocation is known and stable, the control unit can calibrate themeasurement to determine where the roving instrument is located. Thelocation of the roving instrument is very accurate—even usingelectrical-potential measurements—because the tissue characteristicsthat negatively affect those measurements are minimized. Because theroving instrument and antenna reference instruments are in the sametissue, the tissue characteristics can be disregarded, as bothinstruments are equally affected, and the position location system, invarious illustrative embodiments, analyzes the difference between thetwo.

Referring now to the drawings, where like or similar elements aredesignated with identical reference numerals throughout the severalviews, and referring, in particular, to FIG. 1, it is a schematicillustration of the distal portion of antenna reference instrument 100,in accordance with an illustrative embodiment of the invention. Antennareference instrument 100 can be any medical instrument that can beadapted to be inserted into the thorax of a subject and is associatedwith at least two location sensing systems. For example, as shown inFIG. 1, antenna reference instrument 100 can include multiple electrodes130 for sensing current, voltage, or impedance, as well aselectromagnetic sensor 120 for sensing an electromagnetic field. Antennareference instrument 100 can include a catheter system, a pacemaker leadsystem, an implantable cardioverter defibrillator lead system, or anyother suitable medical device, depending on the particular embodiment.

As stated above, antenna reference instrument 100, in some embodiments,includes a catheter system. In some embodiments, the thickness of thecatheter lies in the range of 5 to 7 French. As shown in FIG. 1, thedistal end of antenna reference instrument 100 can be curved, althoughthis is not required. In some embodiments, the distal end of antennareference instrument 100 is fixed, and in other embodiments the distalend of antenna reference instrument 100 has an adjustable deflection.

In some embodiments, distal cap electrode 110 is gold, platinum, silver,or any other suitable material for sensing electrical fields and/orapplying electrical energy. Distal cap electrode 110 can be located atthe distal tip of antenna reference instrument 100 or any other suitablelocation near the tip of the distal end of antenna reference instrument100. In some embodiments, antenna reference instrument 100 does notinclude distal cap electrode 110. In some embodiments, instead of distalcap electrode 110, antenna reference instrument 100 includes a temporaryor permanent pacing lead with fixation devices including, but notlimited to, screws or permanent implantation anchors. One benefit ofusing a more permanent lead device is that, in follow-up procedures, aphysician can connect to the already implanted lead, which provides aknown location for antenna reference instrument 100.

In some embodiments, multiple electrodes 130 are made from gold,platinum, silver, or any other suitable material for sensing electricalfields. While FIG. 1 depicts four electrodes 130, antenna referenceinstrument 100 can include any number of electrodes 130. A typical rangefor the number of electrodes 130 is 1 to 21, though, in someembodiments, more than 20 electrodes can be used. Multiple electrodes130 can be evenly or unevenly spaced along the catheter, depending onthe particular embodiment.

Electromagnetic sensor 120 can be a single coil, as shown in FIG. 1, orelectromagnetic sensor 120 can include multiple coils. Electromagneticsensor 120 can be made of copper, platinum, gold, silver, or any othersuitable metal for sensing electromagnetic fields.

In use, antenna reference instrument 100 can be inserted into the heartof a subject. The insertion point can be the femoral artery in the groinarea or any suitable insertion point for a cardiovascular procedure onthe subject. Once antenna reference instrument 100 is inserted into theheart, electromagnetic sensor 120 senses an electromagnetic fieldapplied, in some embodiments, to the thorax area of the subject.Multiple electrodes 130 can measure current, voltage, or impedance whenelectrical energy is applied to the thorax area of the subject.

FIG. 2 is a depiction of position sensing system 200, according to anillustrative embodiment of the invention. FIG. 2 depicts subject 210,electromagnetic field generator 220, electromagnetic field 230, monitor240, control unit 250, connector breakout box 260, guiding handles 270,electrical-potential field pads 280, roving instrument 290, and antennareference instrument 100. In some embodiments, position sensing system200 is used in a cardiovascular cathlab or operating theatre where othermedical instruments, devices, and systems may be present and/or used.

Subject 210 can include a human, animal, or any other suitable subjecthaving a heart.

Electromagnetic field generator 220 emits electromagnetic field 230. Insome embodiments, electromagnetic field generator 220 is aligned nearsubject 210 such that electromagnetic field 230 emitted fromelectromagnetic field generator 220 engulfs the thorax area of subject210.

As shown in FIG. 2, monitor 240, in some embodiments, displays agraphical representation of the heart as it beats in subject 210.Monitor 240 can display where roving instrument 290 and antennareference instrument 100 are located within subject 210 in relation tothe subject's heart. Monitor 240 can be configured to display thesubject's heart as it beats (dynamically), statically, or not to showthe subject's heart at all. Monitor 240 can be configured to displayantenna reference instrument 100 alone, in relation to the subject'sheart, in relation to one or more roving instruments 290, in relation toboth the subject's heart and one or more roving instruments 290, or notat all. Monitor 240 can be configured to display roving instrument 290alone, in relation to the subject's heart, in relation to antennareference instrument 100, in relation to other roving instruments 290,in relation to the subject's heart and/or one or more other rovinginstruments 290 and/or antenna reference instrument 100, or not at all.In some embodiments, position sensing system 200 includes multipleroving instruments 290, which can also be displayed on monitor 240 inany of the combinations described above.

Monitor 240 can be any suitable monitor for displaying static or dynamicimages. In some embodiments, position sensing system 200 may not includemonitor 240. In other embodiments, position sensing system 200 caninclude multiple monitors 240.

In some embodiments, monitor 240 can be a touchscreen such that monitor240 can receive input via options displayed on the screen, allowing theoperator to choose the desired display configuration.

Control unit 250 can be connected to monitor 240 and connector breakoutbox 260, as shown in FIG. 2. Control unit 250 is described in moredetail below in connection with FIG. 3.

As shown in FIG. 2, in some embodiments, connector breakout box 260 isconnected to control unit 250, electromagnetic field generator 220,electrical-potential field pads 280, roving instrument 290, and antennareference instrument 100. In other embodiments, connector breakout box260 can also be connected to other devices and instruments that are usedfor the procedure. For instance, connector breakout box 260 can beconnected to an RF generator, an ultrasound imaging device, anesophageal temperature probe, an electrocardiogram recording device, anx-ray device, a Computed Tomography (“CT”) device, a Magnetic ResonanceImaging (“MRI”) device, a Positron Emission Tomography (“PET”) device,an Optical Coherence Tomography (“OCT”) device, and/or any other deviceused for the procedure.

As shown in FIG. 2, antenna reference instrument 100 can be a device,the distal end of which can travel through the artery system of subject210 into the heart while navigation handle 270 remains outside subject210. The physician can use navigation handle 270 to guide the distal endof antenna reference instrument 100 to the desired location withinsubject 210. The usable length of antenna reference instrument 100 istypically 65 to 110 centimeters, in some embodiments, although in otherembodiments antenna reference instrument 100 may be longer than 110centimeters or shorter than 65 centimeters. As shown in FIG. 1, antennareference instrument 100 can have multiple sensors, such as one or moreelectromagnetic sensors 120 and one or more electrodes 130.

As shown in FIG. 2, roving instrument 290 can also include navigationhandle 270, which can remain outside subject 210. The physician can usenavigation handle 270 to guide the distal end of roving instrument 290to the desired location within subject 210. Roving instrument 290 caninclude at least one electrode for sensing current, voltage, orimpedance within subject 210. While a single roving instrument 290 isshown in FIG. 2, multiple roving instruments 290 may be used in someembodiments.

Electrical-potential field pads 280 can be placed on the surface ofsubject 210. FIG. 2 depicts five electrical-potential field pads 280,however there may be more or fewer than five. Electrical-potential fieldpads 280 generate electrical current through subject 210, whichgenerates electrical fields that can be sensed by electrodes 130 onantenna reference instrument 100 and the electrodes on roving instrument290. Electrical-potential field pads 280 can be placed on subject 210such that the electrical fields generated engulf the thorax area ofsubject 210. For example, electrical-potential field pads 280 can sendcurrent through subject 210 from right armpit to left armpit, neck togroin, and front to back such that there is an effective X,Y,Zcoordinate system of electrical current running through subject 210.

In use, according to one embodiment, control unit 250 can instructelectromagnetic field generator 220 through connector breakout box 260to generate electromagnetic field 230 that engulfs the thorax area ofsubject 210. Control unit 250 can instruct electrical-potential fieldpads 280 to generate an electrical current through the thorax area ofsubject 210, as described above.

Electromagnetic sensor 120 in antenna reference instrument 100 can senseelectromagnetic field 230, and electromagnetic sensor 120 can send asignal to control unit 250 through connector breakout box 260. Controlunit 250 can determine position coordinates of antenna referenceinstrument 100 based on the signal from electromagnetic sensor 120 inantenna reference instrument 100. Measurements taken from theelectromagnetic localization system can be taken in millimeters. In someembodiments, three-dimensional minimum and maximum locations can also becalculated and recorded. Though antenna reference instrument 100 is in astable location—often the coronary sinus, but antenna referenceinstrument 100 may also be located in the fossa ovalis, high rightatrium, right ventricular apex, or any other stable location—somemovement of antenna reference instrument 100 is normal because of bloodflow, heartbeat, and breathing of the subject. The minimum and maximumthresholds can be any number, but the movement typically does not exceed1 centimeter.

Electrodes 130 in antenna reference instrument 100 can measure theimpedance, voltage, and/or current generated by electrical-potentialfield pads 280. Electrodes 130 can send an electrical-impedance and/orelectrical-potential value to control unit 250 through connectorbreakout box 260. Control unit 250 can determine position coordinates ofantenna reference instrument 100 based on the electrical-impedanceand/or electrical-potential value. In some embodiments, control unit 250determines absolute position coordinates of antenna reference instrument100 using electrical-potential.

The electrodes in roving instrument 290 are used to measure theimpedance, voltage, and/or current generated by electrical-potentialfield pads 280. The electrodes permit control unit 250, throughconnector breakout box 260, to determine a value for the measuredelectrical impedance and/or electrical potential. In some embodiments,control unit 250 measures the electrical-potential difference and/or theelectrical-impedance difference between that measured at antennareference instrument 100 and that measured at roving instrument 290.Based on the measured difference, control unit 250 can calibrate themeasured difference using the determined position coordinates of antennareference instrument 100 and determine the position coordinates ofroving instrument 290.

Control unit 250 can convert the position coordinates for antennareference instrument 100 and roving instrument 290 into an image to bedisplayed on monitor 240.

FIG. 3 is a functional block diagram of a computerized control unit 250,according to an illustrative embodiment of the invention. In FIG. 3, CPU330 and GPU 320 communicate over data bus 370 with each other, I/Omodule 340, storage device 310, electrical-potential field generator350, electromagnetic control unit 360, and memory 380. While FIG. 3depicts only a single CPU, multiple CPUs, a multi-core CPU, or multiplemulti-core CPUs may be present in some embodiments. Similarly, though asingle GPU is depicted in FIG. 3, multiple GPUs, multi-core GPUs, ormultiple multi-core GPUs may be present in some embodiments. In someembodiments, CPU 330 and GPU 320 can be configured to processinstructions in parallel.

Storage device 310 can include, for example, hard disk drives, storagearrays, network-attached storage, tape-based storage, optical storage,flash-memory-based storage, or any other suitable storage device for usein a computer system. While FIG. 3 depicts a single storage device 310,multiple storage devices may be present in some embodiments.

I/O Module 340 facilitates communication with external devices thatcommunicate with control unit 250. For example, I/O module 340 canfacilitate communication with monitor 240 or connector breakout box 260.

In some embodiments, electrical-potential field generator 350 is amodule in control unit 250 that controls electrical-potential field pads280. For example, electrical-potential field generator 350 can controlthe current flowing through the subject between electrical-potentialfield pads 280, which generates an electrical-potential field in subject210. In an illustrative embodiment, electrical-potential field generator350 can create three separate signals, distinguishable by somecharacteristic such as frequency, phase, or time so that an X, Y, and Zsignal can be separated out to determine position coordinates of thesensing electrode.

Electromagnetic control unit 360 can be a module in control unit 250that controls electromagnetic field generator 220. Electromagneticcontrol unit 360 can control the intensity of electromagnetic field 230,as well as turn electromagnetic field generator 220 on and off.

Memory 380 may include, without limitation, random access memory(“RAM”), read-only memory (“ROM”), or flash memory. While FIG. 3 shows asingle memory, in some embodiments multiple memory devices includingcombinations of types may be used. In one embodiment, as shown in FIG.3, memory 380 includes executable program instructions conceptualized asfunctional modules, including electromagnetic localization module 382,electrical-potential/electrical-impedance localization module 384, datastorage module 386, movement sensing module 388, calibration module 390,interface APIs 392, and image rendering module 394. In otherembodiments, the program instructions may be divided into more or fewermodules, and the functional boundaries among the modules can differ fromwhat is indicated in FIG. 3.

Electromagnetic localization module 382 determines position coordinatesof instruments, including antenna reference instrument 100, that includeelectromagnetic sensor 120. In some embodiments, electromagneticlocalization module 382 converts the signals from electromagnetic sensor120 into X, Y, and Z position coordinates.

Electrical-potential/electrical-impedance localization module 384determines position coordinates of instruments, including antennareference instrument 100 and roving instruments 290, that include one ormore electrodes 130. In some embodiments,electrical-potential/electrical-impedance localization module 384converts the signals from electrode 130 into X, Y, and Z positioncoordinates.

Data storage module 386 controls the storage of data, including, withoutlimitation, position coordinates or images and data from the manydevices that I/O module 340 communicates with, as described above.

Movement sensing module 388 recognizes movement of antenna referenceinstrument 100 beyond the predetermined threshold described above. Insome embodiments, if antenna reference instrument 100 moves, thephysician can be notified through a visual or audio alert. The physiciancan move antenna reference instrument 100 back to the stable locationwithin the predetermined threshold. In some embodiments, the newlocation of antenna reference instrument 100 can be used, and an offsetcan be applied to recalibrate the stored images and data for accuratedisplay of the locations of antenna reference instrument 100 and rovinginstrument 290.

Calibration module 390 calibrates the measured differences inelectrical-potential or electrical-impedance between antenna referenceinstrument 100 and roving instrument 290. Within the calibration module390, various mathematical operations are performed. In some embodiments,a three-space coordinate system can be created with voltage values ineach orthogonal (anterior-posterior, inferior-superior, and laterally)axis. For example, electrical-potential field pads 280 can sendelectrical current through subject 210 from right armpit to left armpit,neck to groin, and front to back such that there is an effective X, Y, Zcoordinate system of electrical current running through subject 210.Each axis can have a different carrier frequency. In one embodiment, theX-axis frequency is 30 kHz, the Y-axis frequency is 31 kHz, and theZ-axis frequency is 32 kHz, although other carrier frequencies can beused. A composite voltage can be measured as a difference between anelectrode on roving instrument 290 and an electrode 130 on antennareference instrument 100. A Fourier transformation can be performed onthe composite voltage to extract the separate X, Y, and Z voltagemeasurements corresponding to the X, Y, Z coordinate system. Thesereal-time X, Y, and Z voltage measurements can be placed into a memorybuffer and averaged over varying periods of time to smooth out anyinherent noise in the system and provide the operator with variouslevels of sensitivity of roving-instrument motion, depending on theoperator's haptic preference.

Similarly, in some embodiments, electrical-impedance differences aremeasured between an electrode on roving instrument 290 and an electrode130 on antenna reference instrument 100. A Fourier transformation can beperformed on the composite impedance measurement to extract the separateX, Y, and Z impedance measurements corresponding to the X, Y, Zcoordinate system created by the electrical-potential field pads 280.Buffering and smoothing calculations can be performed to ensure noisecancellation and varying levels of roving instrument motion feedback.

Interface APIs 392 provide interfaces between control unit 250 and otherdevices, including, without limitation, an x-ray device, an RFgenerator, an ultrasound imaging device, an esophageal temperatureprobe, an electrocardiogram recording device, a Computed Tomography(“CT”) device, a Magnetic Resonance Imaging (“MRI”) device, a PositronEmission Tomography (“PET”) device, an Optical Coherence Tomography(“OCT”) device, and/or any other device used in a cardiovascularprocedure.

FIG. 4a is an illustration, according to an illustrative embodiment ofthe invention, of monitor 240. Monitor 240 includes a rendered image ofantenna reference instrument 100, the subject's heart 405, and rovinginstrument 290.

In some embodiments monitor 240 can display the heart dynamically suchthat the subject's heart 405 is shown as beating on monitor 240substantially in time with the subject's true heartbeat. Monitor 240 canalso display the movement of roving instrument 290 in substantiallyreal-time as the physician moves roving instrument 290. The renderedimage of antenna reference instrument 100 can also be shown insubstantially real-time.

As described above, monitor 240 can be any suitable display monitor foruse with a computer system, including without limitation a CRT, atouchscreen, an LCD, a plasma, or an LED display.

FIG. 4b is an illustration, according to another illustrativeembodiment, of monitor 450. In this embodiment, the images displayedinclude not only the subject's heart in the heart display 455, but alsoinclude ECG data display 460, x-ray display 465, ablation data display470, ultrasound display 475, esophageal data display 480, and otherpatient data display 485.

In one embodiment, the data displays described above are all updated bycontrol unit 250. For example, as control unit 250, via Interface APIs392, communicates with external devices such as the ultrasound imagingdevice and receives updated imaging information, GPUs 320 render theimages and send the rendered images via I/O module 340 to ultrasounddata display 475 on monitor 450.

FIG. 5 is a flowchart of a method for determining the positioncoordinates of roving instrument 290 in accordance with an illustrativeembodiment of the invention. At 520, electromagnetic field 230 isapplied to the thorax of a subject. In some embodiments, electromagneticcontrol unit 360 in control unit 250 sends a signal to electromagneticfield generator 220 that causes electromagnetic field generator 220 toemit electromagnetic field 230.

At 530, antenna reference instrument 100 is inserted into the heart ofthe subject. In some embodiments, the insertion point is the femoralartery in the groin area of the subject. From there, antenna referenceinstrument 100 is guided through the vasculature to the subject's heart.

At 540, roving instrument 290 is inserted into the thorax cavity of thesubject. In some embodiments, the insertion point is the same as theinsertion point for antenna reference instrument 100. However, theinsertion point can include any suitable insertion point that allowsaccess to the thorax cavity of the subject.

At 550, position coordinates of antenna reference instrument 100 aredetermined based on sensing electromagnetic field 230. In someembodiments, electromagnetic sensor 120 in antenna reference instrument100 detects electromagnetic field 230 that was applied to the thoraxarea of the subject at 520. The electromagnetic sensor 120 conveys asignal to control unit 250. Electromagnetic localization module 382interprets the signal and converts the signal into position coordinatesof antenna reference instrument 100.

At 560, the electrical-potential and/or electrical-impedance differencebetween antenna reference instrument 100 and roving instrument 290 ismeasured. The electrodes 130 in antenna reference instrument 100 and theelectrodes in roving instrument 290 each convey a signal to control unit250. Electrical-potential/electrical-impedance localization module 384interprets the signal and measures the electrical-potential and/or theelectrical-impedance difference.

At 570, the position coordinates of roving instrument 290 are determinedby calibrating the electrical-potential difference or theelectrical-impedance difference between antenna reference instrument 100and roving instrument 290 using the determined position coordinates ofantenna reference instrument 100. Calibration module 390 uses theposition coordinates of antenna reference instrument 100 determined at550 and the measured electrical-potential and/or electrical-impedancedifference measured at 560 to calibrate the difference and determine theposition coordinates of roving instrument 290.

FIG. 6 is a flowchart of a method for determining the positioncoordinates of roving instrument 290 in accordance with an illustrativeembodiment of the invention. As in the embodiment discussed inconnection with FIG. 5, Blocks 520-570 are preformed. In someembodiments, at 620 additional position coordinates of antenna referenceinstrument 100 are determined in parallel with Block 550. This canprovide redundant absolute location tracking of antenna referenceinstrument 100. At 620, electrodes 130 in antenna reference instrument100 convey a signal to control unit 250.Electrical-potential/electrical-impedance localization module 384interprets the signal and converts it into position coordinates ofantenna reference instrument 100.

FIG. 7 is a flowchart of a method for displaying dynamic images of thelocalized instruments in accordance with an illustrative embodiment ofthe invention. Starting from Block 570 in FIG. 5 or FIG. 6, at 710,multiple images of the heart from systole through diastole are stored ina memory. The images may be captured from any of the external devicesthat communicate with control unit 250. For example, the images can becaptured from an ultrasound imaging device, an x-ray device, an MRIdevice, and/or any other imaging device. Once captured by control unit250, data storage module 386 stores the images on storage device 310.

At 720, the dynamic images of the heart are displayed on monitor (240,450) corresponding to the subject's heart's phase, such that the imagesare displayed in substantially real-time with the beating heart of thesubject. Image rendering module 394 utilizes GPU 320 to render imagesfor display on monitor (240, 450) and correlates the display to occur insubstantially real-time with the heart's phase by utilizing input fromthe external devices that provide data indicating the phase of theheart, such as ECG data.

At 730, the roving instrument image is also rendered on monitor (240,450), in this embodiment. Image rendering module 394 utilizes GPU 320 torender images for display on monitor (240, 450) and correlates thedisplay to occur in substantially real-time as roving instrument 290moves.

FIG. 8 is a flowchart of a method for correcting the display if antennareference instrument 100 moves outside of a predetermined threshold, inaccordance with an illustrative embodiment. In this embodiment, Blocks520, 530, 540, 550, 560, and 570 remain the same as in FIGS. 5 and 6. At820, the calibrated measured electrical-potential and/orelectrical-impedance difference is applied to previously recordedposition coordinates of roving instrument 290. Calibration module 390can check for previously recorded position coordinates of rovinginstrument 290 and apply the calibration such that when the image ofroving instrument 290 is rendered, it appears in the proper positionbecause the position coordinates are properly calibrated in reference toantenna reference instrument 100.

At 830, the location of antenna reference instrument 100 is checked todetermine whether it moved outside a predetermined threshold. If antennareference instrument 100 moved sufficiently, the method returns to Block550 and determines the new position coordinates of antenna referenceinstrument 100 based on sensing electromagnetic field 230 throughelectromagnetic sensor 120 in antenna reference instrument 100. In someembodiments, the position of antenna reference instrument 100 is trackedredundantly using both electromagnetic and electrical-potentialpositioning techniques. As described above, a predetermined thresholdcan be chosen because the beating of the subject's heart as well as thesubject's breathing will cause antenna reference instrument 100 to moveapproximately 1 centimeter, which is considered normal. However, ifantenna reference instrument 100 slips from its substantially stablelocation, the rendered images of roving instrument 290 will no longer beaccurate without a recalibration. Once antenna reference instrument 100moves, an offset can be applied to calibrate all the images to the newantenna reference instrument 100 location, allowing all location data tobe accurate as displayed on monitor (240, 450). In this manner, shiftsin position of antenna reference instrument 100 during the procedure canbe compensated for.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Where methods and/or flowcharts described above indicatecertain events and/or flow patterns occurring in a certain order, theordering of certain events and/or flow patterns may be modified. Whilethe embodiments have been particularly shown and described, it will beunderstood that various changes in form and details may be made.

For instance, in some embodiments multiple roving instruments may beused. In those embodiments, multiple measurement steps can be done todetermine each roving instrument's location. Those measurement steps canbe done in parallel, but they need not be done in parallel, depending onthe embodiment.

Although various embodiments have been described as having particularfeatures and/or combinations of components, other embodiments arepossible having a combination of any features and/or components from anyof the embodiments as discussed above. For example, whileelectromagnetic and electrical-potential or electrical-impedancelocalization methods were used throughout this disclosure, anycombination of those systems may be used. Additionally, other types oflocalization systems could be used.

In conclusion, the present invention provides, among other things,systems and methods for localizing medical instruments within a subjectduring cardiovascular medical procedures. Those skilled in the art canreadily recognize that numerous variations and substitutions may be madein the invention, its use, and its configuration to achievesubstantially the same results as achieved by the embodiments describedherein. Accordingly, there is no intention to limit the invention to thedisclosed exemplary forms. Many variations, modifications, andalternative constructions fall within the scope and spirit of thedisclosed invention as expressed in the claims.

What is claimed is:
 1. A position sensing system, comprising: anelectromagnetic field generator; a distal portion of an antennareference instrument adapted to be introduced minimally invasively intoa living coronary sinus of a beating heart of a subject, the distalportion of the antenna reference instrument including at least oneelectromagnetic sensor and at least one electrode and having anadjustable deflection when located within the living coronary sinus; atleast one roving instrument adapted to be introduced into a thoraxcavity of the subject, the at least one roving instrument including atleast one electrode; and a control unit configured to: with the distalportion of the antenna reference instrument located within the livingcoronary sinus, determine position coordinates of the antenna referenceinstrument based on an electromagnetic signal from the electromagneticfield generator sensed by the at least one electromagnetic sensor whenthe electromagnetic sensor is disposed within the coronary sinus; withthe distal portion of the antenna reference instrument located withinthe living coronary sinus, measure an electrical-potential differencebetween the at least one electrode of the antenna reference instrumentand the at least one electrode of the at least one roving instrument;and with the distal portion of the antenna reference instrument locatedwithin the living coronary sinus, calibrate the measuredelectrical-potential difference using the determined positioncoordinates of the antenna reference instrument to determine positioncoordinates of the at least one roving instrument.
 2. The positionsensing system of claim 1, wherein the antenna reference instrumentincludes a catheter system designed for placement in and cannulation ofthe coronary sinus.
 3. The position sensing system of claim 2, whereinthe catheter system has a usable length of 65-110 centimeters, athickness of 5-7 French, and one of a fixed and an adjustable deflectionof 0-180 degrees, and wherein the catheter system includes 2-20electrodes for sensing electrocardiograms and an integratedelectromagnetic sensor that includes at least one metallic coil.
 4. Theposition sensing system of claim 1, wherein the antenna referenceinstrument includes at least one of a pacemaker and an implantablecardioverter defibrillator (“ICD”) lead system designed for placement inand cannulation of the coronary sinus.
 5. The position sensing system ofclaim 4, wherein at least one of the pacemaker and the ICD lead systemhas a usable length of 65-110 centimeters, a thickness of 5-7 French,and one of a fixed and an adjustable deflection of 0-180 degrees, andwherein at least one of the pacemaker and the ICD lead system includes2-20 electrodes for sensing electrocardiograms and an integratedelectromagnetic sensor that includes at least one metallic coil.
 6. Theposition sensing system of claim 1, wherein the control unit isconfigured to, with the distal portion of the antenna referenceinstrument located within the living coronary sinus, determineadditional position coordinates of the antenna reference instrumentbased on electrical-potential sensed by the at least one electrode ofthe antenna reference instrument to provide redundant tracking of theantenna reference instrument.
 7. The position sensing system of claim 1,further comprising a monitor connected to the control unit, wherein thecontrol unit is configured to: store multiple images of the heart fromsystole through diastole in a memory; display, on the monitor and withthe distal portion of the antenna reference instrument located withinthe living coronary sinus, a dynamic image of the heart corresponding tothe heart's phase using the stored multiple images of the heart; anddisplay, on the monitor, a dynamic image of the at least one rovinginstrument showing the location of the at least one roving instrumentwith respect to the heart using the determined position coordinates ofthe at least one roving instrument.
 8. The position sensing system ofclaim 1, wherein the control unit includes: at least one centralprocessing unit; and at least two graphical processing units; whereinthe at least two graphical processing units are on separate graphicscards, and the control unit is configured to parallel processmathematical computations on the at least one central processing unitand the at least two graphical processing units.
 9. The position sensingsystem of claim 1, wherein the control unit is configured to:communicate via an application programming interface with at least onedevice, the at least one device including at least one of an RFgenerator, an ultrasound imaging device, an esophageal temperatureprobe, and an electrocardiogram recording device; retrieve informationfrom the at least one device; and store the information in a memory. 10.The position sensing system of claim 1, wherein the control unit isconfigured to: determine movement of the antenna reference instrumentoutside of a predetermined threshold to a new location when the distalportion of the antenna reference instrument is located within the livingcoronary sinus; determine position coordinates of the antenna referenceinstrument at the new location based on (1) sensing an electromagneticsignal from the electromagnetic field generator using the at least oneelectromagnetic sensor when the electromagnetic sensor is located withinthe living coronary sinus; with the distal portion of the antennareference instrument located within the living coronary sinus, measurean electrical-potential difference between the at least one electrode ofthe antenna reference instrument at the new location and the at leastone electrode of the at least one roving instrument; with the distalportion of the antenna reference instrument located within the livingcoronary sinus, calibrate the measured electrical-potential differenceusing the determined position coordinates of the antenna referenceinstrument at the new location to determine position coordinates of theat least one roving instrument; and with the distal portion of theantenna reference instrument located within the living coronary sinus,apply the calibrated measured electrical-potential difference topreviously recorded position coordinates of the at least one rovinginstrument.
 11. A position sensing system, comprising: anelectromagnetic field generator; a distal portion of an antennareference instrument adapted to be introduced minimally invasively intoa living coronary sinus of a beating heart of a subject, the distalportion of the antenna reference instrument including at least oneelectromagnetic sensor and at least one electrode, the distal portion ofthe antenna reference instrument having an adjustable deflection whenlocated within the living coronary sinus; at least one roving instrumentadapted to be introduced into a thorax cavity of the subject, the atleast one roving instrument including at least one electrode; and acontrol unit configured to perform the following steps when the distalportion of the antenna reference instrument is disposed in the coronarysinus of the beating heart of the subject: determine first positioncoordinates of the antenna reference instrument based on (1) a firstelectromagnetic signal from the electromagnetic field generator sensedby the at least one electromagnetic sensor when the electromagneticsensor is disposed within the coronary sinus; determine second positioncoordinates of the antenna reference instrument based on (1) a secondelectromagnetic signal from the electromagnetic field generator sensedby the at least one electromagnetic sensor when the electromagneticsensor is disposed within the coronary sinus; identify a reference shiftof the antenna reference instrument when a comparison of the firstposition coordinates to the second position coordinates exceeds apredefined threshold; measure an electrical-potential difference betweenthe at least one electrode of the antenna reference instrument and theat least one electrode of the at least one roving instrument; and inresponse to the identified reference shift, calibrate the measuredelectrical-potential difference using the determined second positioncoordinates of the antenna reference instrument to determine positioncoordinates of the at least one roving instrument.
 12. A positionsensing system, comprising: an electromagnetic field generator; a distalportion of an antenna reference instrument adapted to be introducedminimally invasively into a moving coronary sinus of a living heart of asubject, the distal portion of the antenna reference instrumentincluding at least one electromagnetic sensor and at least oneelectrode, the distal portion of the antenna reference instrument havingan adjustable deflection such that the at least one electromagneticsensor and the at least one electrode of the antenna referenceinstrument are deflectable relative to each other; at least one medicalinstrument adapted to be introduced into the thorax cavity of thesubject, the at least one medical instrument including at least oneelectrode; and a computerized control system configured to: with thedistal portion of the antenna reference instrument disposed within themoving coronary sinus, determine first position coordinates of theantenna reference instrument based on an electromagnetic signal from theelectromagnetic field generator sensed by the at least oneelectromagnetic sensor when the at least one electromagnetic sensor isdisposed within the moving coronary sinus; with the distal portion ofthe antenna reference instrument disposed within the moving coronarysinus, determine second position coordinates of the antenna referenceinstrument based on electrical-potential sensed by the at least oneelectrode of the antenna reference instrument when the at least oneelectrode of the antenna reference instrument is disposed within themoving coronary sinus; with the distal portion of the antenna referenceinstrument disposed within the moving coronary sinus, measure anelectrical-potential difference between the at least one electrode ofthe antenna reference instrument and the at least one electrode of theat least one medical instrument; and with the distal portion of theantenna reference instrument disposed within the moving coronary sinus,calculate the position of the at least one medical instrument based onthe measured electrical-potential difference and the first positioncoordinates.
 13. The position sensing system of claim 12, wherein thecomputerized control system is further configured to: with the distalportion of the antenna reference instrument disposed within the livingcoronary sinus, detect a reference shift of the antenna referenceinstrument to a new location based on the electromagnetic signal sensedby the at least one electromagnetic sensor; with the distal portion ofthe antenna reference instrument disposed within the living coronarysinus, determine third position coordinates of the antenna referenceinstrument based on an electromagnetic signal from the electromagneticfield generator sensed by the at least one electromagnetic sensor at thenew location; with the distal portion of the antenna referenceinstrument disposed within the living coronary sinus, calculate anoffset between the first position coordinates and the third positioncoordinates; with the distal portion of the antenna reference instrumentdisposed within the living coronary sinus, apply the offset to thecalculated position of the at least one medical instrument; and with thedistal portion of the antenna reference instrument disposed within theliving coronary sinus, apply the offset to recorded position coordinatesof the at least one medical instrument.
 14. The position sensing systemof claim 12, wherein the antenna reference instrument includes apacemaker.
 15. The position sensing system of claim 12, wherein theantenna reference instrument includes an implantable cardioverterdefibrillator lead.